Flow control



Jan. 20, 1970 W. M. PRESTON FLOW CONTROL Filed Nov. 16, 1967 9mm Pu.

INVENTOR. W. M. PRESTON A TTORNEVS United States Patent "ice 3,490,240FLOW CONTROL William M. Preston, Borger, Tex., assignor to PhillipsPetroleum Company, a corporation of Delaware Filed Nov. 16, 1967, Ser.No. 683,564 Int. Cl. E21f 17/16; B65g 5/00; F16k 21/18 US. Cl. 61-.5 8Claims ABSTRACT OF THE DISCLOSURE Flow control apparatus is provided foruse with underground storage systems. Signals are established whichrepresent changes in the rate of flow of fluids withdrawn from thecavern. When such changes exceed predetermined values, fluid flows areterminated. Control apparatus is also provided to terminate the fluidflows when the flow rates are outside predetermined ranges.

This invention relates to flow control systems for use in conjunctionwith the underground storage of fluids.

It is common practice to store certain fluids, such as liquefiedpetroleum gas, in underground storage caverns. When hydrocarbons arestored in caverns of this type, it is common practice to use brine fordisplacement of the hydrocarbon from the cavern. On the filling cycle,hydrocarbon is pumped down to displace the brine, which can be stored ina reservoir at the surface. In both of these operations it is importantto know when the cavern is filled with either the hydrocarbon or thebrine so that the delivery conduit can be closed to prevent withdrawalof mixtures of the two materials. This avoids the possibility of theremoved hydrocarbon being contaminated with brine and the possibility ofdelivering flammable hydrocarbon to the brine reservoir.

In US. Patent No. 3,056,265 there is disclosed a control system for usein underground storage operations of this type. The flow rate of thewithdrawn liquid is measured, such as by measuring the pressuredifferential across an orifice in the flow conduit, and the withdrawalof liquid is terminated when the indicated flow rate exceeds apredetermined value. In this manner, delivery of a miX- ture of twofluids is prevented. While the flow system described in this patent isquite effective in certain operations, a need exists for a moreversatile control system. This is particularly true when it is desiredto store and remove fluids at diflerent rates of flow.

In accordance with the present invention, a control system is providedwhich is based on measurements of changes in the rates of flow of fluidswithdrawn from an underground storage cavern. This control system can beemployed on both the hydrocarbon and brine removal conduits. The controlsystem serves to shut down flow of withdrawn fluid Whenever a rate ofchange of flow in excess of the predetermined value is measured. Thisprevents mixing of the product streams, and permits operation of thesystem at various flow rates. In addition, control mechanism is providedin accordance with this invention for shutting down flows in thedelivery conduits whenever the measured flow is greater or less thanpreselected limits. This provides automatic shutdown in the event ofleakage or other malfunctions in the storage system.

Accordingly, it is an object of this invention to provide an improvedmethod of controlling the operation of underground storage systems.

Another object is to provide novel control apparatus for use withunderground storage systems.

Other objects, advantages and features of the invention should becomeapparent from the following detailed description in conjunction with theaccompanying drawing in which:

3,490,240 Patented Jan. 20, 1970 FIGURE 1 is a schematic representationof an underground storage system having the control apparatus of thisinvention associated therewith.

FIGURE 2 is a schematic circuit drawing of a first embodiment of thecontrol apparatus which utilizes electrical elements.

FIGURE 3 is a schematic representation of a second embodiment of thecontrol apparatus which utilizes pneumatic elements.

Referring now to the drawing in detail and to FIGURE 1 in particular,there is shown a subterranean storage cavern 10. Caverns of this typecan be formed by conventional mining procedures or by solution miningwhen appropriate structures, such as salt domes, are available. Asillustrated in the drawing, cavern 10 is partially filled with a volumeof hydrocarbon 11 which floats on a volume of a more dense immiscibleliquid 12, such as brine. Cavern 10 is connected to the surface of theearth by a suitable access hole into which a hollow casing 13 iscemented. The lower end of casing 13 terminates near the top of thestorage cavern 10 to permit introduction and withdrawal of thehydrocarbon to be stored. A tubing 14 extends through casing 13 andterminates at its lower end adjacent the bottom of the storage cavern.Brine is introduced and withdrawn through tubing 14. Conduits 16 and 17are connected to casing 13 and tube 14, respectively, at the surface topermit introduction and withdrawal of the hydrocarbon and brine. Aconduit 18, which has a pump 19 and a check valve 20 therein,communicates with conduit 16 to introduce hydrocarbon to be stored. Aconduit 21 which has a pump 22 and a check valve 23 therein,communciates With conduit 17 to permit introduction of brine. A conduit24, which has a valve 25 therein, communicates with conduit 16 to permitwithdrawal of hydrocarbon. A conduit 26, which has a valve 27 therein,communicates with conduit 17 to permit withdrawal of brine.

When it is desired to store hydrocarbon in cavern 10, pump 19 isactuated to introduce the hydrocarbon from a source of supply, notshown. Valve 27 is opened to permit withdrawal of brine which isdisplaced upwardly through tubing 14 when the hydrocarbon is introducedinto the cavern through casing 13. When it is desired to withdrawnhydrocarbon from the cavern, pump 22 is actuated and valve 25 is opened.Brine is then introduced into the cavern through tubing 14, andhydrocarbon is withdrawn through casing 13 and conduits 16 and 24. Inaccordance with this invention, a flow transducer 30 and a control valve31 are disposed in conduit 16. Transducer 30 is connected to a flowtransmitter 32 which provides an output signal that is representative ofthe rate of flow through conduit 16. This signal is transmitted to arecorder-controller 33. Recorder-controller 33 operates in the manner tobe described hereinafter to shut valve 31 when certain conditions occur.Similarly, a flow transducer 34, a flow transmitter 35, arecordercontroller 36, and a valve 37 are associated with conduit 17.

A first embodiment of the control system, which utilizes electricalelements, is illustrated in greater detail in FIG- URE 2. Flowtransmitter 32a, which can be either flow transmitter 32 or 35 of FIGURE1, provides an output electrical signal which is proportional to therate of flow of fluid through conduit 24, for example. The first outputterminal of transmitter 32a is connected to the junction betweenresistors 38 and 39 which form two adjacent arms of a current dividingbridge network 40. The same output terminal of transmitter 32a isconnected by means of a variable resistor 42, which has a capacitor 43connected in parallel therewith, to the junction between resistors 44and 45 Which form the remaining arm of bridge 40. A relay coil 46 isconnected across the second opposite terminals of bridge 40. Relay coil46 serves to close a switch 47 when current of predetermined magnitudeflows through the relay coil. Closure of switch 47 connects a currentsource 48 to a motor control circuit 49. Motor control circuit 49connects a power source 51 to a motor 52 when the motor control circuitis energized. Motor 52 closes valve 31 of FIGURE 1 when motor controlcircuit 49 is energized.

The control elements of FIGURE 2 are employed when brine is beingintroduced into cavern to displace hydrocarbon through conduits 16 and24. In normal operation, the brine is introduced into the cavern bymeans of gravity plus whatever energy is required from pump 22 totransport the brine to tubing 14. The head of brine usually issuflicient to displace the hydrocarbon because cavern 10 is normallylocated a substantial distance below the surface. As the brine fillscavern 10 to displace hydrocarbon, there is a slow decrease in the rateof hydrocarbon withdrawal due to the changing differential pressure headexerted by the brine. When the interface between hydrocarbon 11 andbrine 12 reaches the bottom of casing 13, brine enters the casing andflows upwardly toward outlet conduit 16. Since the brine introduced intothe cavern has a much smaller volume of hydrocarbon to displace at thistime, the differential pressure head and the flow detected by transducerdecreases at a substantially greater rate. The control system of FIGURE2 senses this decrease in flow rate and actuates motor 52 to close valve31, thereby preventing brine from being withdrawn through conduit 24.

Bridge is balanced initially, under normal flow conditions, byadjustment of resistor such that any current flow through relay coil 46is less than that required to energize the relay. As long as arelatively uniform rate of flow is detected, the circuit remains in thiscondition. However, any rapid fluctuation in the rate of flow changesthe potential applied across bridge 40 and energizes relay coil 46 toclose switch 47. This results from the electrical delay action imposedby resistor 42 and capacitor 43. Under relatively steady stateconditions of flow, the same potential is applied to both of the bridgeinput terminals. A change in the output from transmitter 32a appearsinstantly at the junction between resistors 38 and 39, but the change atthe junction between resistors 44 and 45 is delayed because of resistor42 and capacitor 43. Thus, a rapid change in flow through conduit 16 isdetected by the circuit of FIGURE 2, and this serves to close valve 31.Motor control 49 is adapted to energize motor 52 to drive valve 31 to afully closed position when an input pulse is received by switch 47 beingclosed momentarily. For example, a latching relay can be energized bysuch a pulse. This latching relay can energize motor 52 to move valve 31to a closed position. A Limitorque motor can be used for this purpose,for example.

Bridge 40 is employed in the circuit of FIGURE 2 to permit accurateadjustment of the current flow through relay coil 46 for difierentpotential differences across the bridge. However, in some applicationsrelay coil 46 can merely be connected across resistor 42 and capacitor43. Adjustable resistor 42 permits the sensitivity of the controlcircuit to be varied.

The control circuit of FIGURE 2 also serves to close valve 31 in theevent the fiow through conduit 16 exceeds a first preselected value orfalls below a second predetermined value. To this end, a variableresistor 53 and a relay coil 54 are connected between the first outputterminal of transmitter 32 and ground. When relay coil 54 is energized,a switch 55 is closed. This switch is connected in parallel with switch47 such that closure of switch 55 energizes motor 52 to close valve 31.Resistor 53 is adjusted such that relay coil 54 is not energized unlessthe current exceeds a predetermined value, which is indicative of anexcess flow through conduit 16. A variable resistor 56 and a relay coil57 are also connected between the first terminal of transmitter 32a andground.

Resistor 56 is adjusted such that sufiicient current normally flowsthrough relay coil 57 to keep the relay energized. The relay isdeenergized only when the indicated flow decreases below a preselectedvalue. When this occurs, a switch 58, which also is connected inparallel with switch 47, is closed to energize motor 52.

The low flow shut-down provided by relay coil 57 and switch 58 serves asa back up system to relay coil 46 and switch 47 Once casing 13 is filledwith brine, there is substantially no pressure ditferential so that theflow through conduit 16 decreases to a very low value. This closes valve31 in the event that a failure has occurred in the primary controlcircuit. The high flow shut-down provided by relay coil 54 and switch 55is activated in the event of a conduit rupture which permits rapid flowof volatile hydrocarbons from the cavern.

A normally closed switch 60 is connected in the circuit between currentsource 48 and motor control 49 to permit the motor control to bedeactivated during normal start-up procedures or at any other time. Analarm 61 is connected in parallel with motor control 49 to alert anoperator when valve 31 is closed. The output signal from flowtransmitter 32a is also applied to a flow recorder 62 which can be of atype which provides a record of the cumulative fiow through conduit 16.A flow meter 63 is provided with two individual flow indicating pointers64 and 65. This meter is connected to the two end terminals of resistor42 such that pointer 64 represents the output signal from flowtransmitter 32a and pointer 65 represents the potential between resistor42 and bridge 40. Under steady state conditions, these two pointersregister the same flow. A diiference occurs only when there is a changein flow, as previously described.

The apparatus of FIGURE 2 can also be employed as recorder-controller 36on conduit 17. In this application, an increase in the rate of flow isdetected when hydrocarbon enters tube 14 at the completion of thefilling cycle. Bridge 40 is balanced initially such that this increasein flow results in current fiow through relay coil 46. In a similarmanner, the high flow shut-down feature serves to back up the action ofrelay coil 46.

In FIGURE 3 there is shown a second embodiment of therecorder-controller which utilizes pneumatic components. Transmitter 32bprovides an output pneumatic pressure which is representative of therate of flow through the conduit to which the recorder-controller isconnected. This pressure is transmitted by a conduit 69 to first andsecond bellows 70 and 71. A conduit 72, which has an adjustable valve 73therein, is connected to a third bellows 74 which opposes bellows 70.The first end of a lever arm 75 is connected to the junction betweenbellows 70 and 74. Lever arm 75 is adapted to rotate about an adjustablepivot point 76 in response to relative expansion and contraction of thetwo bellows. The second end of lever arm 75 is connected to a switch 47which corresponds to switch 47 in FIGURE 2. Under steady state operatingconditions, bellows 70 and 74 receive substantially the same pneumaticpressure and switch 47' remains open. A sudden increase in the rate offiow results in a momentary difference between the two pressures becauseof the presence of restrictor valve 73. This causes rotation of leverarm 75 such that switch 47' is closed. Pivot point 76 can be positionedon either side of the rotatable lever arm, depending on the particularapplication to which the recorder-controller is to be used. It ispositioned below the lever arm, as illustrated, when an increase in flowis to actuate the control valve. It is positioned above the lever armwhen the converse is true.

A reference pneumatic pressure is supplied to a fourth bellows 77 by aconduit 78 which has an adjustable pressure regulator 79 therein.Bellows 71 and 74 oppose one another such that the relative movementtherebetween rotates lever arms 80 and 81 about respective pivot points82 and 83. Lever arms 80 and 81 actuate respective switches 55' and 58'which correspond to switches 55 and 58 of FIGURE 2. By adjusting thereference pressure supplied to bellows 77, these two switches can beactuated when high and low flow rates are detected. Switches 47', 55 and58' of FIGURE 3 actuate a control circuit of the type illustrated inFIGURE 2. An indicator 63' is connected to conduit 72 on the two sidesof valve 73.

In the specific embodiment of this invention described herein wherebrine is used to displace hydrocarbon, flow detector 30 canadvantageously be a turbine meter and fiow detector 34 can be a magneticflow meter. However, other detectors can be employed. The choice ofdetector depends to a large extent on the nature of the fluid beingmetered.

An important feature of this invention resides in the control systemwhich responds to the rate of change of fiow rather than the actualflow. This use of the derivative of fiow permits the shut-down system tobe operated at different rates of fiow without any adjustment beingrequired, as long as changes in fiow rates are gradual. Anotherimportant feature of this invention resides in the safety back upcontrols.

While the invention has been described in conjunction with presentlypreferred embodiments, it obviously is not limited thereto.

What is claimed is:

1. In a system for storing liquids, which system includes an undergroundstorage cavern, first conduit means extending from the surface of theearth to a region inside and near the top of the cavern for introducingand Withdrawing a first liquid, and second conduit means extending fromthe surface of the earth to a region inside and near the bottom of thecavern for introducing and withdrawing a second liquid which isimmiscible with and of greater density than the first liquid; controlapparatus comprising first means associated with one of said conduitmeans to establish a first signal which is representative of the rate offlow of liquid through said first conduit means, a valve in one of saidconduit means, second means responsive to said first signal to establisha second signal when said first signal changes and means responsive tosaid second signal when said second signal reaches a predeterminedmaximum value to close said valve.

2. The apparatus of claim 1 wherein said first means establishes a firstelectrical signal between first and second terminals, the magnitude ofsaid first electrical signal being representative of the rate of flow isfluid through said one conduit means; said second means comprises aresistor and a capacitor connected in parallel with one another betweensaid first and second terminals; and wherein said means to control saidvalve comprises means responsive to a predetermined potential differencebe tween said first and second terminals to close said valve.

3. The apparatus of claim 1 wherein said first means establishes a firstpneumatic signal, the magnitude of which is representative of the rateof flow through said one conduit means; and wherein said second meanscomprises first and second bellows connected in opposition to oneanother, means to apply said pneumatic signal directly to one of saidbellows, conduit means having a restrictor therein to apply saidpneumatic signal to the second of said bellows, and means responsive tothe relative positions of said bellows to establish said second signal.

4. The apparatus of claim 1, further comprising means reponsive to saidfirst means to close said valve when said first signal exceeds a firstpredetermined value, and means responsive to said first means to closesaid valve when said first signal is less than a second predeterminedvalue.

5. The apparatus of claim 4 wherein said means to close said valve whensaid first signal exceeds a predetermined value comprises a first relaywhich is energized when said first signal exceeds said firstpredetermined value, and means responsive to said first re'lay beingenergized to close said valve; and wherein said means to close saidvalve when said first signal is less than said second predeterminedvalue comprises a second relay which is deenergized when said secondsignal is less than said second predetermined value, and meansresponsive to said second relay being deenergized to close said valve.

6. The apparatus of claim 4 wherein said means to close said valve whensaid first signal exceeds said first predetermined value and said meansto close said valve when said first value is less than said secondpredetermined value comprise a first bellows, means to apply saidpneumatic signal to said first bellows, a second bellows in oppositionto said first bellows, means to apply a reference pneumatic signal tosaid second bellows, and means responsive to relative move'ments of saidbellows to close said valve when said bellows are displaced bypredetermined amounts.

7. The apparatus of claim 1 wherein said first means is associated withsaid first conduit means, and further comprising third means associatedwith said second conduit means to establish a third signal which isrepresentative of the rate of flow of liquid through said second conduitmeans, a second valve in said second conduit means, fourth meansresponsive to said third signal to establish a fourth signal when saidthird signal changes at a predetermined rate, and means responsive tosaid fourth signal to close said second valve.

8. The apparatus of claim 7, further comprising means responsive to saidfirst means to close the first mentioned valve when said first signalexceeds a first predetermined value, means responsive to said firstmeans to close said first mentioned valve when said first signal is lessthan a second predetermined value, means responsive to said third meansto close said second valve when said third signal exceeds a thirdpredetermined value, and means responsive to said third means to closesaid second valve when said third signal is less than a fourthpredetermined value.

References Cited UNITED STATES PATENTS 2,938,383 5/1960 Blackburn 61.5 X3,056,265 10/1962 Swinney 6l.5 3,068,884 12/1962 Naul et al 6l-.5 X

JACOB SHAPIRO, Primary Examiner U.S. Cl. X.R. 137343, 386, 561

